Is it possible to let this work for the transmission server in COS, when COS acts as firewall/router with public adress on it? And eventually, is it possible to not let it influence with other services like mail server/flexshare/owncloud? Or is this only possible to acheive with an physical internal client computer?

My solution is to turn off the proxy. If you have a relative fast ISP-connection and do not pay by byte, proxy is not essential. I have had this trouble on several (actually all) installs, and all is fixed just by turning off the proxy. I do not know what the fault is, but there is nothing wrong we have done, for sure. We are talking fresh installs on rather powerful xeon-servers with lines from 80/80mbps up to 500/500mbps. With proxy it took ages to load even simple pages, and picture-heavy pages could take a minute to load. Without proxy it takes <1 second. I tried some tuning of proxy on one of the servers, but there was minimal difference. I cannot say anything but "something" has happened with proxy that makes it useless. In older versions proxy almost never gave the slightest hickup, it was very stable and on slower internetlines a very good help. On a school we had 250 concurrently used PC's sharing a 2mbps line. With proxy it worked pretty OK, without several complained about timeouts etc. But this is some 15 years ago :-P

Great app! A small glitch is that it is not set to autostart, and if it is set to be one of the modules in the dashboard (https://servername:81/app/dashboard) the webview will hang, until the service is started.

Now, I have so much trouble with the frustrating content filter in 7x (slow performance, not able to view several sites, in general far to buggy)

That's strange, the Content Filter engine (DansGuardian) is the exact same version and the newer Web Proxy (Squid) is a much needed update. Maybe a DNS issue? Or slow response times from antivirus? This may not be relevant to you, but the Community Edition doesn't handle more than 10-20 users.

Peter,

Thanks alot for your answer. I have now been in touch with support, and I have got solutions to downgrade to 6.x, if I want. I'll consider it.
Now, I have tried several installs of 7.x, to eliminate any faults done by me. I have used quite some hours in logs, trying to figure out whats going wrong, but I cannot find the specific fault. Several (Norwegian) sites offering paid videos (i.e tv2.no, who use https, contacts several secure/license/certificate-sites to figure out if I have paid for viewing the videoes, as I have of course), will not work properly as long as content filter is on. My ISP (Altibox.no fiber, 80/80 mbps) seems to have everything in order, included DNS. Well, if I change DNS manually to google DNS, OpenDNS or other), it starts working again for a short term, then its stops working, with some faultcodes hinting to loss of data in short moments. If I use 6.x, it works without issues. Even if I tick OFF all possible "brakes" in content-filter, it still makes trouble. Not only video-sites, but also some more ordinary web-pages, some schemes not willing to work... Bah! :-D
Now, this is not my only concern using 7.x . Loss of samba (not starting, looses connection with LDAP), loss of community edition of Owncloud in marketplace, and no use of the new samba (beta), because of no connection to Zarafa, makes me think it's easier for me to stick with 6.x, ATM. I enjoy some thinkering to get stuff working, but this time I belive there is to much job to get "stuff" to work properly (read: my wife is complaining for not being able to view what he wants on the TV, not able to access files, bla-bla-bla-complaining-bla-bla-bla), so... ;-P
Hardware should be adequate, Xeon L3426 CPU, 4GB ECC RAM (not able to find new correct RAM for this Intel serverboard), 1GB HW-RAID, server-quality GB-NICs, all approved by RH... 8 users, seldom more than 3-4 concurrently; Plex stealing most of CPU/RAM, but within sensible amounts.

Now, I have so much trouble with the frustrating content filter in 7x (slow performance, not able to view several sites, in general far to buggy)

That's strange, the Content Filter engine (DansGuardian) is the exact same version and the newer Web Proxy (Squid) is a much needed update. Maybe a DNS issue? Or slow response times from antivirus? This may not be relevant to you, but the Community Edition doesn't handle more than 10-20 users.

Now, I have so much trouble with the frustrating content filter in 7x (slow performance, not able to view several sites, in general far to buggy)

That's strange, the Content Filter engine (DansGuardian) is the exact same version and the newer Web Proxy (Squid) is a much needed update. Maybe a DNS issue? Or slow response times from antivirus? This may not be relevant to you, but the Community Edition doesn't handle more than 10-20 users.